This invention relates, in general, to semiconductor products, and more particularly, to manufacturing semiconductor devices.
At the present time, ions or dopants that are implanted into gallium arsenide substrates are not effectively and efficiently measured. These measurement inadequacies cause several problems, such as extended time delays for qualification of implanters, imprecise measurement of implanted dopants, and use of expensive gallium arsenide wafers.
Conventionally, measurement of ions implanted into gallium arsenide substrates is a multistep process. Typically, the gallium arsenide substrate is implanted with a specific dose or a specific number of ions. The substrate is then capped with a silicon nitride, a silicon dioxide, or a silicon oxynitride layer and subsequently annealed. The anneal activates the implanted ions and makes the implanted ions electrically measurable. The capping nitride layer is then stripped off the gallium arsenide substrate, thereby exposing the gallium arsenide substrate. A four-point probe is then used to measure the electrical activity in the gallium arsenide substrate that is a consequence of the implanted ions. This electrical activity, typically measured as ohms/square, is a result of the dose or the number of ions implanted into the gallium arsenide substrate. However, it should be realized that each ste is associated with a certain variability, and by having many steps the individual variability of each step is summed into a large total variation, thereby resulting in inaccurate measurement of implanted dopants.
For example, the anneal cycle, necessary for electrically activating the implanted ions, often does not produce complete activation of the implanted ions, thereby producing inaccurate electrical measurements which does not be directly correlated with the implanted ions. Inaccurate electrical measurements of the implanted ions are also caused by variations in substrate that the ions are implanted into. Additionally, high temperature furnace anneals may cause unwanted redistribution of dopants used to achieve desired electrical resistivity in the gallium arsenide substrate, thereby causing inaccurate electrical measurement of the ions implanted into the gallium arsenide wafer.
It can be readily seen that conventional measurement methods for determining dose of ion implantation into gallium arsenide substrates have severe limitations. Also, it is evident that the processing conditions required for measurement of ion implantation into gallium arsenide substrates adds to measurement variability. Additionally, because of the long processing time to prepare gallium arsenide substrates for measurement, it is not possible for immediate confirmation of an ion implanted dose from an ion implanting system. Therefore, a method for allowing a more accurate measurement of ion implantation for gallium arsenide substrates, as well as a shorter processing time for gallium arsenide substrates, would be highly desirable.